KABUL, Afghanistan  Afghan officials say that the next phase of transferring security from NATO to Afghan control will begin in two months and aims to cover nearly 90 percent of the country’s population.

The transition, which began in early 2011, is slated to give Afghan forces full responsibility for security by the end of 2014 when most NATO troops will have withdrawn.

Ashraf Ghani Ahmadzai, who heads a transition commission, said at a news conference Monday that three earlier phases have been generally successful. He said Afghan security forces now are responsible for safeguarding the security of 75 percent of the population.

Misgivings persist about the readiness of Afghan forces, although their numbers have grown rapidly over the past year to more than 330,000. They now shoulder most combat operations.